In 1670 the name Toronto made its first appearance in history as 'lac de Taranteau' on a map of southern Ontario drawn by the French priest Father Rene de Brenhant de Galinee.
Galinee's map of 1670 (English translation)
The 1670 map referred to Lake Simcoe, not the area known as Toronto today. As maps were copied and passed from hand to hand in the following years, the name was miscopied.
French map from around 1675 showing the future city’s name as "Taronto." "Lac de Taronto" indicates the present Lake Simcoe.
By the 1720s, Toronto was accepted as referring to a trading post on Lake Ontario at the mouth of the Humber River, where present-day Toronto is located.
The meaning of the word has been a subject to much discussion. The most popular interpretation originated with the nineteenth-century historian Henry Scadding, who claimed that it derived from a Huron word meaning 'to be plenty,' so that Toronto means 'plenty of people' or, as Scadding put it, 'meeting place.'
This interpretation is not accepted by many historians today, who are better versed in native languages. Current interpretations suggest the origin of the word Toronto in a Mohawk term for fish trap or weir, which were a noticeable feature of life around Lake Simcoe.
More on early Toronto.
Steckley, John, "Toronto ... or is that Taranteau?" in Explore Historic Toronto, Toronto Historical Board, November 1992.